Electrical cables are used in conjunction with a printed wiring board (PWB) to conduct electrical signals between a location on the PWB and another location in the circuit. Such electrical cables typically include a center conductor surrounded by a dielectric or insulating layer. In a coaxial cable, the cable also includes a shield layer surrounding but electrically isolated from the center conductor.
In modern electronic devices, such as portable radios, surface mount techniques are used to minimize the area required for mounting of components such as electrical cables. Components and cable terminations are soldered directly to the surface of the PWB, eliminating the space and expense required for plated-through solder holes. Also, surface mounted components may be placed automatically by a pick and place machine, reducing cost and time for manufacture and improving quality. Surface mounting increases the density of component placement on a PWB and reduces the size of the PWB.
Cables are difficult to handle, both for surface mounting and for automated pick and place. Pick and place machines require a relatively large, flat area on the outer surface of a component for engagement by a vacuum pick and place tool. Cables are typically round in cross section and are too small in diameter to be reliably picked up by the vacuum tool. Moreover, when such cables are soldered to the surface of the printed wiring board, the cables tend to roll because of the round cross section of the cable and because of soldering of the cable's center conductor to the PWB surface rather than insertion of the center conductor through a plated through hole.
The difficulty in handling such cables increases the expense associated with their use in any design. Handling and mounting such cables, rather than being automated, requires manual labor. Manual labor is more expensive, takes longer and is less reliable than automated methods. Cables and PWB assemblies which are damaged during handling and mounting of cables must be reworked or discarded.
Another component which requires special handling during assembly of a printed wiring board is a shield. A shield is a conductive element, typically box shaped, placed over a portion of circuitry on a PWB to protect the circuitry from electromagnetic radiation originating outside the shield or to protect adjacent circuits from electromagnetic energy originating inside the shield. As electronic circuitry has been miniaturized and packed ever more tightly together, more and more shields are required for electrical isolation in the finished assembly.
Shields are typically removably mounted to the surface of the printed wiring board. Removability is desired because, with a shield in place, the circuitry beneath the shield is inaccessible for test or repair. When the shield is removed, the circuitry may be tested and repaired. Following the repair, the shield is replaced for proper operation of the assembly.
To permit a shield to be removed and subsequently replaced, shields are held in place using shield clips. A shield clip is a component which mounts to the PWB and mechanically engages the shield to retain the shield in place. For the same reasons that other components are surface mounted on a PWB, including eliminating the space and expense required for plated-through solder holes and more densely packing circuitry on the PWB, shield clips are surface mounted on the PWB, too.
Accordingly, there is a need in the art for apparatus for surface mount attachment and for automated pick and place of a cable and shield in an electronic assembly.